On July 10, NASA’s Juno spacecraft flew closer to Jupiter’s famous “Great Red Spot” than ever before, capturing images of the ancient and gargantuan storm from only 5,600 miles away as it skimmed over the gas giant’s cloud tops.

This was Juno’s first close encounter with Jupiter’s most iconic feature, the 10,000-mile wide atmospheric gyre that has been raging near the planet’s equator for at least a couple of centuries—and possibly much longer.

In all that time, the Spot—large enough to encompass two or three planet Earths—has generated more questions than answers. Why has it lasted so long? How deep into Jupiter’s thick atmosphere and gaseous depths do its roots plunge? What causes its namesake coloration? Why has it been slowly shrinking over past decades?

It will take some time to analyze the flyby data collected by Juno’s eight science instruments, so answers to questions like these won’t come immediately, but the preliminary images are as tantalizing as they are stunning.

Since arriving at Jupiter a little over a year ago, the Juno mission has focused on other Jovian mysteries. Getting a close view of the Great Red Spot was somewhat of a bonus.

Surprises from Cloud Tops to the Core

We have long known that Jupiter is wrapped in clouds of ammonia, but microwave data from Juno has revealed an unexpectedly strong concentration of the stuff in a band around Jupiter’s equator—not to mention other areas of the planet that appear to have little. The equatorial band of ammonia may also run very deep, perhaps reaching a depth of around 200 miles into Jupiter’s interior—the distance between San Francisco and San Luis Obispo!

These findings suggest weather systems based on ammonia, which circulate and concentrate the chemical in different areas and at different altitudes and depths, maybe like how Earth’s weather systems transport and concentrate water. Imagine getting caught in a caustic rainstorm of eye-burning ammonia!

Juno has also challenged earlier assumptions and models of the structure of Jupiter’s interior. It was previously thought that Jupiter is made up of smooth, uniform layers beneath its outer patina of cloud systems. Older textbook illustrations usually show a thin outer layer of liquid hydrogen wrapped around a deeper, thicker layer of metallic hydrogen, all enclosing a solid core at the center.

However, measurements of Jupiter’s gravitational field, made by detecting tiny variations in Juno’s altitude as it flies through gravitational “bumps in the road” along its orbit during close passes, have suggested that the layers within are not smooth global blankets, but are irregular—maybe warped and blobby envelopes, as opposed to smooth spherical shells.

The “choppy” irregularity of the internal layers suggests that the nature of Jupiter’s deep core may be different than previously thought. The core was assumed to be a solid sphere nested smoothly within the surrounding layers—like the yolk of a hard-boiled egg set within the egg white surrounded by the shell.

But Juno’s findings hint that the core may be “sticky,” or “fuzzy,” interacting strongly with and agitating surrounding materials as the planet and its layers rotate. Think of how the blades of a blender interact with your raspberry smoothie….

And we have long known that Jupiter is surrounded by a powerful magnetic field, which emerges from inside the planet and extends far into the surrounding space. Earlier models explaining this magnetic field assumed it was generated deep within Jupiter, near its core, like the dynamo that drives Earth’s magnetic field.

But in Juno-fashion, this idea has been turned on its head. Not only is Jupiter’s magnetic field much stronger than predicted before Juno’s arrival, its shape—variations in the field across different regions—suggest its origin is much closer to Jupiter’s surface, not deep within.

Mega-Cyclones

The Great Red Spot is famous for being a storm that could swallow two or three planet Earths—and it is the biggest atmospheric gyration on Jupiter by far.

But Juno has discovered many previously unseen cyclone systems—some up to the size of a single Earth, perhaps. These cyclones went unseen before Juno’s arrival because they are located in Jupiter’s polar region, which Juno specializes in.

Juno’s “Life Spiral”

Juno orbits Jupiter once every 53 days, swinging along an elliptical path that carries it through a long, slow loop 5 million miles from the planet, then into a rapid plunge to within 2,600 miles of Jupiter’s polar region. The orbit was designed to allow the spacecraft to spend as little time as possible within the intense radiation belts close to Jupiter, over concerns of the radiation damaging its sensitive instruments and electronics.

The strategy seems to be working, for Juno appears to be in the pink of health.

Ultimately, however, Juno’s winding orbit will become a “death spiral,” and the spacecraft will steer into Jupiter’s atmosphere and burn up. This robot version of a Viking funeral has been done before. Juno’s own predecessor, Galileo, met this end back in 1995, and Cassini is slated to crash and burn in Saturn’s atmosphere this September.

This disposal technique is carried out to prevent the spacecraft from crashing into a possibly life-bearing moon, like Europa or Enceladus, and contaminating it with any dormant Earth microbes they might be carrying.

Juno’s demise has been scheduled for February 2018, so we still have several months left to unravel Jupiter’s mysteries—a good thing, since Jupiter has turned out to be far more mysterious than we ever thought!

After 13 years and over 27 miles exploring the dry sea bed of Mars’ Meridiani Planum, NASA’s record-shattering rover Opportunity is still going.

Originally slated for a 90-day tour of Mars, Opportunity’s mission has been extended multiple times, making it the longest-operating robot on the red planet. The next longest running, Opportunity’s twin Spirit, lasted 8 years, and the Curiosity rover, also prospecting for signs of Mars’ watery past since 2012, has traveled a little over 5 miles so far.

Now, after it poked about the rim of the giant Endeavour Crater for the last six years, NASA is preparing to send Opportunity on a challenging and risky (dare we say “heroic”?) trek down a fluid-carved canyon that may have been formed by flowing water in the distant past.

If this canyon, Perseverance Valley, was the locale of an ancient mega-cascade, what a fitting final mission for a rover that has spent its long career looking for signs of water.

Why Has Opportunity Lasted So Long?

From a three month mission to 13 years—how has this little rover lasted so long? Did engineers simply underestimate the lifespan for this rolling robot? Or, is this like a Disneyland line where wait times never match expectations?

Neither. The 90-day expiration date has less to do with the robot’s durability, and more to do with the overall mission plan. Scientists estimate the minimum time a mission should run in order to achieve its goals; anything beyond that is a bonus.

After the initial mission duration is reached, it may be given an extension, and at the end of that, perhaps another. Part of the decision for whether and how long to extend a mission is based on funding, but the potential rewards of exploring further also factor in—as has been the case with Opportunity several times.

A Robot Dedicated to Finding Signs of Water

Opportunity began its career in 2004 when it rolled to a stop at the bottom of the 70-foot wide Eagle Crater, in the flat expanse of Meridiani Planum.

Right out of the box the rover spied evidence of past water, in the form of layers of sulfate-rich rock that appear to have been laid down in shallow water in Mars’ past. NASA operators were concerned that the rover might not be able to climb out of the crater. But if it hadn’t rolled to a stop there, it might never have seen sedimentary rock exposed on the inner crater wall.

Farther along its travels, Opportunity discovered tiny round, gray spherules of hematite, a mineral that can form by accretion in acidic water. Dubbed “blueberries” because they appeared blue in false-colored images captured by Opportunity’s microscopic camera, further study of their distribution in the Meridiani rocks suggested that these spherules most likely did form in water, and not by some other process, such as volcanism or wind action.

Opportunity found further stratigraphic evidence of past water in the exposed sedimentary layers of Burns Cliff in Endurance Crater, not far from its landing site. The layered rocks told a story of water that appeared and dried up episodically, indicating that the region underwent wet and dry cycles over time.

Though the signs of past water popped up in several places along Opportunity’s path, the chemical evidence told us that the water was probably acidic, and not favorable enough to support life. So, past water, yes, but could anything have lived in that water?

This question remained open until Opportunity reached Endeavour Crater in 2011.

There, Opportunity discovered a vein of minerals containing calcium, sulfur, and water—identified as gypsum—sticking out of the soil along the crater rim. The vein was likely deposited by mineral-rich water flowing through cracks in the rock. That water would have been less acidic than previously sampled locations, with pH levels closer to neutral.

This was the first indication in Meridiani Planum of a past watery environment suitable to support life—at least life forms as we know them on Earth.

Next for Opportunity: Taking the Plunge

For six years Opportunity has loitered safely on the rim of the Endeavour Crater, nursing a failing front-wheel steering system but quietly continuing its very extended mission.

Now, however, NASA has decided that exploring the fluid-carved Perseverance Valley is worth the risk. Opportunity could discover that torrents of water once cascaded down the wall of Endeavour Crater and move in for a closer look.

The rover spent time examining the spillway leading down into Perseverance Valley before commencing its deeper plunge down stream, to whatever fate awaits it.

And who knows? Opportunity has surprised everyone with its longevity and marathon crawl across the Martian surface, so I’m not willing to rule out its safe arrival at the bottom of the mysterious canyon.

Four decades ago, NASA launched two robotic spacecraft, Voyagers 1 and 2, on a mission to cruise by the giant planets of the outer solar system on sweeping trajectories that would ultimately carry them far beyond.

Today, both spacecraft are still functioning, sending back data from the cold, dark reaches of the frontier of interstellar space. Voyager 2 is over 10.6 billion miles from the sun, 115 times farther than Earth. Voyager 1 is almost 13 billion miles out—a distance that takes radio signals, traveling at the speed of light, over 19 hours to traverse!

Voyager Mission Recap

The Voyagers were launched in 1977—Voyager 1 on September 5 and Voyager 2 on August 20, so their 40th anniversaries in space are close at hand.

Voyager 1’s objective was to explore Jupiter and Saturn, and gave us our first detailed images of Jupiter’s four large Galilean moons. It also made a close flyby of Saturn’s largest moon, Titan, giving us our first look at the moon’s cold, thick, hydrocarbon-smog-laced atmosphere.

Voyager 2 also passed by Jupiter and Saturn, before cruising onward to the cold and mysterious “ice giant” worlds Uranus and Neptune—which still have not been visited by any other spacecraft.

Pushing the Frontiers of Space

Upon completion of their primary missions, both Voyagers coasted onward to ever greater distances, having achieved escape velocity from the sun’s gravitation. And though they spent their earliest years of exploration traveling within the orbital plane of the solar system’s planets, the Voyagers’ final planetary encounters flung them in different directions. Voyager 1 is heading northward away from the plane of the solar system while Voyager 2 is going south.

Since leaving the realm of planets, the Voyagers have been monitoring the physical conditions within the heliosphere, the extended “bubble” of gas, plasma, and magnetic fields emanating from the sun and blowing outward into space, called the solar wind. The goal of this extended phase of the Voyagers’ mission was to find the boundary between the solar wind’s influence and the environment of interstellar space: the heliopause.

From Earth, we cannot detect that boundary—much in the way that you cannot “see” the boundary between Earth’s atmosphere and outer space by standing on the ground and looking up. To find where space beings, you must send up a rocket to measure the pressure and temperature of the air.

Voyager 1’s measurements of the solar wind tell us that in August 2012, it did in fact cross the heliopause and enter the frontier of interstellar space, becoming the first human artifact to do so.

Voyager 2 has not yet crossed the heliopause in the direction it is traveling, but when it does, researchers will receive data from two different points in the interstellar realm, which will offer a more detailed picture of the nature of space beyond the influence of the sun.

Built to Survive the Unknown

How have these robotic explorers lasted so long? What machinery in your experience can last forty years with no maintenance, refueling, or recharging?

The Voyagers had to last at least through their primary missions, which in Voyager 2’s case included encounters with four giant planets over a 10-year period. Engineers had to anticipate the harsh conditions their robots might encounter, and plan accordingly—even though the actual conditions around the target planets and in the vast stretches of space between them were largely unknown.

The Voyagers’ sensitive equipment and computer systems are heavily shielded against micrometeorite impacts and high-energy radiation. Critical systems were given multiple redundant backups, so that if a piece of equipment fails a backup duplicate will kick in to replace it.

As for their power supplies, the Voyagers are each equipped with three radioisotope thermoelectric generators, which generate electricity from heat produced by the decay of Plutonium-238. At the time of launch each trio of generators produced 470 Watts, though the output has declined steadily as the Plutonium decays. It is expected that by sometime between 2025 and 2030, power will have fallen below the level needed to run any of the Voyagers’ instruments.

Messengers for ET? Good idea?

Another ride-a-long feature on each Voyager is the “Golden Record,” a gold-plated analog phonograph record carrying information about our world and species in a set of selected sounds and images. The records are intended as combination time capsules and greeting cards, in the event that either spacecraft is recovered by an intelligent alien civilization who can follow the graphical instructions inscribed on the record covers and extract the information on the disks.

There are some who feel it may not be a good idea to randomly fling information of our existence and location into space for any would-be aliens to find–for how could we possibly know what those aliens are like, and what they would do with the information?

Still, the chances of recovery of the tiny, soon-to-be-derelict spacecraft in the vast expanse of interstellar space is exceedingly small, and neither are heading toward any star systems in the near or extended future. Voyager 1 is presently heading in the general direction of a star called Gliese 445, which it will pass within 1.6 light years of in about 40,000 years.

In the meantime, Voyagers 1 and 2 should continue to transmit home their measurements from the interstellar frontier, so may yet teach us a thing or two about our place in the cosmos.

When NASA’s Voyager 1 and 2 spacecraft  left Earth in 1977, they had a mission that was possible only at that very moment in human history. The spacecraft were headed toward two of the outer planets of our solar system, and would use the gravity of one planet to swing themselves toward the next.

It’s the alignment of Jupiter, Saturn, Uranus, and Neptune that make this gravity swing dance possible. This alignment happens only once every 176 years, and it happened just at the time when human space technology was ready to meet the challenge.

When it comes to the Voyager mission, the numbers themselves are cosmic. Voyager 1 is 13 billion miles away from Earth, and counting. Voyager 1 and 2 discovered “The Great Dark Spot” on Neptune and the first active volcanoes on another planet — on Jupiter’s moon, Io. In 2012, Voyager 1 passed across the far end of our solar system to give humanity its first taste of interstellar space.

These were not among the outcomes Ed Stone could have imagined when he and his colleagues at NASA’s Jet Propulsion Laboratory prepped the two Voyagers for launch in 1977. Their mission was a four-year sortie to Jupiter and Saturn — which at the time seemed plenty ambitious. The moon landing was still a fresh memory.

Now in his 80s, Professor Stone, a physicist and National Medal of Science recipient, continues to serve as chief scientist for the program he helped launch. He is also a full-time professor and researcher at Caltech. He spoke with KQED News host Devin Katayama on the occasion of Voyager’s 40th anniversary.

Katayama: Professor Stone, you were in your early forties when Voyager 1 and 2 launched into space. What was the original goal of that mission?

Stone: The original goal was a four-year mission to Jupiter and Saturn and Titan, a moon of Saturn. And we had two spacecraft to give us a higher probability of having at least one making it on that four-year journey to Saturn.

Katayama: So did you ever think the Voyager spacecrafts would last this long?

Stone: None of us knew how long they would last. At the time the space age was only 20 years old.

Katayama: So, 40 years later, what are some of the most important planetary discoveries to date, thanks to the Voyager mission?

Stone: Well, we discovered that nature is much more diverse than we could have imagined. For instance, before Voyager, the only known active volcanoes were here on Earth. And then we found a moon of Jupiter called Io, about the size of our moon, which has ten times more volcanic activity than Earth. So time after time, we’ve discovered that our ‘terracentric’ view of planets and magnetic fields and moons and rings was much too limited.

Katayama: People working in the field might not be surprised to discover how expansive space could be, but has it changed our understanding of the universe?

Stone: We now understand that when bodies form, there are processes by which they can maintain a very active geological life, just as the Earth does. And the way that happens depends on the exact circumstances. So each moon seems to be quite distinct in character.

Katayama: NASA put a message on Voyager for other civilizations in outer space that might one day find it — The Golden Record. What was the thinking behind that?

Stone: It was a form of outreach. It was a declaration that we as a society here on Earth could actually send such a message, which would leave the sun, the solar system, and orbit the center of the Milky Way galaxy for billions of years, long after Earth itself may have ceased to exist.

Katayama: Can you share with us what that message was?

Stone: There were several messages: greetings from different languages on Earth, messages from different cultures, images of various aspects of Earth. The whole idea was to make this a time capsule, or what I call a calling card: the ambassadors Earth has sent to the Milky Way galaxy.

Katayama: I’m curious whether you had any say in what that messaging was.

Stone: The messaging was really determined by Carl Sagan and a small group that he put together. They did this basically over a 6-month period before launch, and it was done independently of what we were all doing, getting ready for launch.

Katayama: I’m curious whether there are any questions you were hoping would be answered by Voyager that have not been answered.

Stone: I think what Voyager has done is inform us well enough to know what interesting questions to ask now. For instance, before Voyager, the only known liquid water was here on Earth, in the ocean. Then we flew by Europa, another moon of Jupiter, which has an icy crust on it which is cracked — very much like ice on an ocean. In fact, that’s what a subsequent mission, Galileo, has shown.

Katayama: The Voyager spacecraft are steadily losing power, and I saw a prediction that NASA will have to turn off all the equipment by 2030. What do you think should come next in terms of probing interstellar space?

Stone: The next step is exploring the heliosphere itself, which is the huge bubble that Voyager left in August 2012. That is going to be done by a mission here on Earth which looks at neutral atoms coming from the outer edges of the heliosphere and from the interstellar medium beyond. That mission is now being launched in 2024. It would be the next stage in understanding the heliospheric bubble that protects all the planets in the solar system, and its interaction with the winds of the other stars as it occurs in interstellar space.

Katayama: What are the biggest questions about the heliosphere that we need to understand?

Stone: We need to understand the size of the heliosphere, because it breathes in and out with the 11-year solar cycle. But it will also change size as the material outside in interstellar space changes over a much longer time scale. So it’s understanding how our solar bubble, which envelops the Earth, interacts and changes as what’s in interstellar space also changes.

Katayama: What does communication between us here on Earth and the Voyager spacecraft look like?

Stone: We listen 24 hours a day; the spacecraft each have a 21-watt transmitter. We get a very slow data rate — it’s 160 bits per second, which is the best we can get from 13 billion miles away.

Katayama: What’s it been like having a hand in such an important mission, and having spent most of your career with Voyager?

Stone: It’s been a remarkable journey. Science is about learning about nature — why it’s there, why it is the way it is. And Voyager has been an overwhelming success in terms of scientific endeavor. But even more than that, the thing that’s wonderful about Voyager is it’s remarkably inspiring to many people, and that’s of great value as well. It turned out to be a very effective way of involving the greater public in the journey, which is a scientific journey of discovery.

Want more Voyager action? Check out ‘The Farthest,’ a new full-length film from PBS. You can live-stream it here.

On September 15, NASA’s flagship robotic explorer, Cassini, will plummet into Saturn’s atmosphere in a fiery burn-up, ending a thirteen-year career of exploring Saturn and its host of remarkable moons.

As Cassini readies itself for the dramatic end-of-mission blow-out, we can take some time to reflect on a few of its most remarkable discoveries and achievements.

Huygens Probe

Early in its mission, in 2005, Cassini dropped the European Space Agency’s Huygens probe onto the surface of Titan, Saturn’s largest moon. This remains the most distant landing in our solar system to date.

Huygens parachuted through Titan’s thick nitrogen atmosphere and hydrocarbon haze, measuring atmospheric pressure, temperature, and composition, as well as recording sounds with a microphone during the nearly 2.5-hour descent.

Huygens captured images of the landscape below as it descended, and pictures from Titan’s surface following its successful landing—the first images from the surface of any object in the outer solar system.

Water on Enceladus

Also in 2005, Cassini discovered plumes of water vapor erupting from the tiny moon Enceladus. The gases, emerging from long crevasses near the south pole, included other chemicals, such as nitrogen, methane, and carbon dioxide.  In 2008, Cassini also detected propane, acetylene, and formaldehyde in the geyser plumes.

Further measurements from several flybys of the moon fueled the hypothesis that Enceladus possesses a saltwater ocean hidden deep under its icy crust. Even more tantalizing, the evidence suggests that there may exist hydrothermal vents spewing hot, mineral-laden water on the ocean’s floor.

This makes Enceladus a very hot prospect in the search for locations beyond Earth that could support some form of life. Hydrothermal vents in our own oceans support thriving communities of life forms.

Saturn’s Dynamic Rings

Cassini’s many years of observations of Saturn’s icon rings have revealed their dynamic nature in ways that single “snapshots,” such as images captured during the brief fly-bys of Voyagers 1 and 2, could not, and in much finer detail.

Not only have scientists analyzed the dusty, icy composition of the rings, they have discovered tiny moons, near and even orbiting within the rings, sculpting the ring material into repeating waves, ropey filaments, and other intricate and beautiful patterns.

Cassini has even seen, in some locations, vertical structures rising in rows of feathery, spiky fringe high above the rings. These features are caused by the passage of a tiny “moonlet” orbiting Saturn nearby, which disrupts the ring’s otherwise flat plane.

An image taken in 2013, showing a bright “knot” within the outermost of Saturn’s bright rings, may prove to be a new moon forming out of the ring material. If so, then Cassini’s ring observations may tell us something about the formation of some of Saturn’s other small, icy moons.

Titan: A Cold, Primordial Earth?

One of the most intriguing characters in the Cassini-Huygens mission is Titan. Saturn’s largest moon happens to be the only one in the solar system with a thick atmosphere. The Voyager missions, passing through the neighborhood in the 1980s, were the first to see Titan’s atmosphere and its obscuring shroud of hydrocarbon “smog.” Cassini, and the Huygens probe, however, have revealed it in rich detail.

Though cold in the extreme, Titan’s dense nitrogen, hydrocarbon-infused atmosphere has proven to support a liquid cycle, analogous to Earth’s water cycle, but dealing in cryogenic liquid methane and ethane instead. Precipitation collecting in extensive river-like drainage networks feed into large lakes and seas, one comparable in surface area to Lake Superior in North America.

Complex hydrocarbons are found on Titan, a product of photo-chemical interactions of sunlight and methane high in the atmosphere. These organic molecules form Titan’s “smog” layer, and precipitate downward to supply the liquid cycle on the surface. Though cold enough to liquefy methane–a gas on Earth–Titan has been likened to a primordial, pre-biotic Earth, and in studying it we may be catching glimpses of our own planet’s beginnings.

Saturn Scrutinized at Close Range in Cassini’s Grand Finale Tour

Cassini is now in the final phase of its so-called “Grand Finale” tour, looping through a wildly eccentric polar orbit that sends it skimming repeatedly between Saturn’s rings and cloud-tops. This final and daring maneuver, Cassini’s “swan song” of Saturn exploration, is giving us our closest, most detailed vistas ever of the gas giant and its famous rings.

Cassini is also making magnetic and gravitational measurements during each close pass that promise to tell us something about Saturn’s internal structure. And, as it makes its ever-tightening swings closer to the atmosphere, it will ultimately sample the planet’s chemistry directly, becoming the first spacecraft to touch the skies of Saturn.

The Final Plunge

When Cassini finally plunges into Saturn, friction with the atmosphere will generate intense heat, and Cassini will be vaporized.

Cassini’s planned incineration is a move by NASA to protect Saturn’s moons from accidental contamination by Earthly microorganisms that could be riding along. (Space agencies NASA and the ESA had also considered the potential for contamination of Titan by the Hugyens probe, but determined that the extremely low temperatures and lack of liquid water made the likelihood practically zero.)

After 20 years in space (seven years traveling to Saturn and 13 years in orbit), Cassini is running low on the rocket fuel used to adjust its trajectory. Once its fuel is depleted, the spacecraft would otherwise become a derelict that could crash into a moon.

With the possibility of life-friendly environments on at least one or two of Saturn’s moons, NASA’s end-of-mission ethic is to safely dispose of the spacecraft to eliminate that possibility.

Farewell, Cassini, and thanks for all the wonders you have brought us!

After 13 years in orbit around Saturn, NASA’s Cassini spacecraft is about to plunge itself into the planet’s atmosphere and disintegrate. NASA decided to put an end to the mission on Friday because the probe is almost out of fuel.

Cassini has provided exquisite details about the second-largest planet in our solar system.

Take the hurricanes at Saturn’s poles, for example. “These hurricanes are large enough they’d cover about half the continental United States, about 50 times larger than a typical Earth hurricane,” says Cassini project scientist Linda Spilker of NASA’s Jet Propulsion Laboratory.

Then there are the remarkable, hexagonal-shaped jet streams at the north pole. They’ve been there since before Cassini arrived in 2004.

“We have jet streams here on the Earth, but they change almost daily,” Spilker says. “So we’re really puzzled. It’s the only place we know of in our solar system that has a long-lived hexagonal jet stream.”

Spilker’s special interest is Saturn’s rings, and she says Cassini has revealed some unexpected things about them. There are places, for example, where the particles that form the rings clump together.

“The clumpiness has a unique character. Sometimes it looks kinda clumpy and speckly, other times it looks streaky,” she says. And in other places, the particles float freely and don’t appear to have any structure.

“How you can keep those areas separated?” she says. “That’s an interesting and curious puzzle.”

For all that Cassini has revealed about Saturn, there are still plenty of mysteries.

“It’s a little bit embarrassing to confess, but we don’t know how long a day is on Saturn,” says Michele Dougherty of Imperial College in London. She’s the scientist in charge of Cassini’s magnetometer, an instrument that measures Saturn’s magnetic field.

“In some ways,” she says, “you can almost use a magnetometer to see inside a planet and get a better understanding of its internal structure.”

Cassini’s final orbits are taking it closer to the planet than ever before. Dougherty is hoping this will let her instrument see a telltale tilt in the magnetic field that should resolve the uncertainty over the length of a Saturnian day. “If we don’t, we might not be able to work out the exact length of a day is on Saturn,” she says.

Some of Cassini’s most interesting discoveries involve Saturn’s moons.

Take Enceladus.

“Enceladus is this little moon. It’s about the size of the United Kingdom,” says Carly Howett of the Southwest Research Institute in Boulder, Colo. Scientists were amazed to see giant plumes of salty water vapor belching from Enceladus’ south pole, suggesting liquid seas under a frosty crust that could maybe, possibly, harbor life.

Howett’s instrument on Cassini, the composite infrared spectrometer, has revealed that the surface of Enceladus is extremely porous. “Much more porous than freshly fallen snow,” she says. “If you were to put your hand on top of this and push down, your hand would go a long way into the surface. It wouldn’t put up much resistance at all.”

That Cassini is still functioning so well after 13 years in orbit isn’t a big surprise to JPL mission engineer Julie Webster. She says the spacecraft came prepared.

“We carry two computers, two radios, two gyroscopes, two sun sensors, two star scanners, so we had our backups,” she says.

A good indication of just how well Cassini has worked is the number of times it’s gone into “safe” mode. When a spacecraft detects some type of software or hardware problem on board, it shuts down all nonessential equipment, turns its main antenna toward Earth and basically calls home to ask for instructions.

“We’ve only done that six times in 20 years, and only twice since 2003,” Webster says. “So most of the ‘safings’ were early as we were learning the spacecraft.”

NASA’s decision to end the Cassini mission has an interesting back story. It seems mission managers were worried that without fuel to change its orbit, the probe could crash into one of Saturn’s moons sometime in the future. The space agency was loath to let that happen, because it can’t be certain that Cassini isn’t carrying some hardy microbial spores from Earth. There’s good reason to believe that some bacteria could survive 20 years in space.

The last thing NASA would want to do is send a future probe to one of Saturn’s moons, only to find it colonized by bacteria from Earth.

The end of Cassini is going to be a sad day for the many thousands of scientists, engineers and technical staff who have worked on the mission.

“I’ve gone through all the stages of mourning, all the stages of grief,” says Webster, who has worked on the mission since its launch in 1997.

“It’s going to a sad day,” agrees Howett, who has been working on the Cassini mission since 2005. “I’m heavily, emotionally invested in this mission in a way that doesn’t normally happen. It’s basically been the backbone of my career.”

Dougherty says she’ll also be sad to see the last radio signal from Cassini. “But it’s going to a really proud moment, too,” she says. “Because the instruments and the spacecraft are still doing spectacularly well, and so to end in this almost blaze of glory that we’re going to end in I think is the way to go.”

Copyright 2017 NPR. To see more, visit http://www.npr.org/.

Space fans are well familiar with the robotic landers and rovers sent to explore Mars, packed with the routine cameras, rock drills, soil scoopers and spectroscopes that we have come to expect from Mars missions.

Now, time for something completely different: a robotic lander that is part stethoscope, part meat-thermometer, and part radar gun!

NASA is moving forward with plans for a May 2018 launch of InSight, a spacecraft designed to investigate how the rocky planets of the inner solar system formed by exploring the interior of the planet Mars.

InSight was originally scheduled to launch in 2016, but a leak in the vacuum enclosure of one of its scientific instruments forced a postponement to the next launch window, when Earth and Mars come closest to each other.

Why is InSight Different and What Can it Tell Us?

Past missions to Mars have focused on the planet’s surface and atmosphere: orbiters mapping the globe and scanning for chemical signatures; landers and rovers scraping and drilling into the soil and rock looking for evidence of past environmental conditions, in some cases even signs of life.

All our scrutiny of Mars’ outward face has shown us that, long ago, Mars was a very different world, maybe even resembling Earth in some ways. In its youth, Mars had a thicker, warmer atmosphere, and a liquid water cycle of precipitation, rivers, lakes and seas.

For years scientists have sought to understand why Mars went from being a possibly life-friendly world billions of years ago to a seemingly dead, dry desert today.  And though clues may be found on its surface, a deeper understanding of the processes involved in the shaping of Mars—and by extension Earth and the other rocky planets—may only be possible with a look inside.

How Will InSight Probe Mars’ Interior?

InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) is equipped with three principal instruments designed to probe the interior of Mars–none of which will take pictures, analyze minerals, or dig up soil samples as other Mars landing missions have done. The only cameras on board InSight will be used primarily to aid in the deployment of the main science instruments.

SEIS

The SEIS (Seismic Experiment for Interior Structure) instrument is a seismometer that will measure vibrations coming from Mars’ interior–sounds produced by quakes, meteorite impacts and other sources of activity. By studying how sound waves travel through Mars, scientists can gain an understanding of its internal structure and history of formation.

SEIS is even capable of detecting disturbances caused by the gravitational tug of Mars’ larger moon, Phobos, as it orbits the planet.

This planetary version of a stethoscope will be placed on the ground near the landing site by a robotic arm, guided to the selected location with a set of cameras.

On Earth, geophysicists use seismometers to learn about the internal structure of our planet. As sound waves are produced by events like earthquakes, they move through the rock and magma of Earth’s different interior layers. The varying density and composition of those layers causes the sound waves to refract, bending the direction they travel.

By measuring how the vibrations travel and bend, scientists can develop a “picture” of the internal structure, not unlike how a sonogram forms a picture of the inside of a human body.

HP3

The HP3 (Heat Flow and Physical Properties Package) instrument will measure the flow of heat from Mars’ core as it escapes through the crust.

The instrument package will be placed near the lander, and a self-hammering spike will pound itself as deep as 5 meters into the ground, like a meat thermometer stuck into a turkey. Trailing behind this “spearhead” will be a tether with temperature sensors strung along its length, spaced 10 centimeters apart.

Variations in temperature measured at different depths underground will show how much and how fast heat is flowing upward through the crust. From these data, the temperature of Mars’ core and the history of its cooling off over time can be estimated.

Mars–like Earth–once had a magnetic field that shielded the planet from the effects of the “solar wind” flowing from the sun. It is now mostly vanished and researchers hope that understanding Mars’ thermal history will reveal what happened.

Earth’s magnetic field shields our planet from the solar wind, and without that protection our atmosphere would experience direct exposure, and slowly be “eroded” away into space.

A collapse of Mars’ magnetic shield, perhaps related to the cooling of its core that generated it, may explain why its atmosphere has mostly disappeared.

RISE

InSight’s “RISE” (Rotation and Interior Structure Experiment) experiment will use the spacecraft’s X-band radio to make measurements of Mars’ rotation.

By measuring the Doppler shift of InSight’s radio transmissions to Earth, precision measurements of Mars’ rotation can be made—in much the same way that the speed of a car can be measured by a police radar gun. Aspects of a planet’s rotation–not just speed of spin, but also cyclic wobbles, the precession  and nutation, of its axis–can tell us what’s going on inside, in terms of internal structure.

Data from the RISE experiment will add to similar measurements made years ago on the Viking and Pathfinder missions, and should give scientists what they need to calculate the size and density of Mars’ core and mantle, furthering our understanding of how rocky planets like Mars and Earth formed.

Other Instruments

In addition to its principal instruments, InSight will carry wind, temperature and pressure sensors to monitor atmospheric conditions at the landing sight, as well as a magnetometer to measure disturbances produced in Mars’ ionosphere.

InSight’s cameras, which are primarily for guiding the placement of the SEIS and HP3 instruments on the ground, will also serve in taking pictures of the surrounding landscape—something we have come to expect from our Mars landers and rovers, even if InSight’s main mission is to look where cameras cannot see.

On September 22, a spaceship visited Earth—NASA can confirm that it wasn’t alien property. It was NASA’s own OSIRIS-REx probe, swinging by Earth in a gravitational “slingshot” maneuver designed to fling it toward a 2018 rendezvous with an asteroid named Bennu.

The spacecraft will become NASA’s first mission ever to visit an asteroid, collect samples of its ancient materials, and return them to Earth for laboratory analysis.

More than merely an asteroid-dust collector, however, this mission aims to give scientists a clearer understanding of the formation of the solar system, the Earth, and the origin of life on our planet.

Launched on September 8, 2016, OSIRIS-REx —which stands for Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer—will arrive at Bennu in August 2018, where it will map the asteroid’s surface in detail, and then graze to within a few meters of its surface to collect dust samples. It will then head back to Earth for an expected return in 2023.

What Can Asteroids Tell Us About Life on Earth?

Asteroids—as well as comets—are the debris left over from the formation of our solar system, about 4.6 billion years ago, and are potential gold mines of information about the early conditions that shaped Earth and the other planets. They formed during the earliest times in the solar system, and have remained largely unchanged since then.

On Earth, geological action and weathering alter terrestrial rocks over time, effectively erasing information about the earliest conditions on our planet. Attempting to reconstruct the environment that led to the origin of life on Earth by studying terrestrial rocks is a bit like trying to perceive an artist’s original painting on a canvass that has been painted over multiple times.

Were Oceans Filled by Asteroids Like Bennu?

Bennu is a roughly 500-meter diameter Near-Earth Asteroid–one whose closest approach to the sun is less than 120 million miles. Not only is it close to Earth and relatively easy to visit, it is a “carbonaceous” asteroid—rich in carbon compounds, as well as other materials like water.

This makes it a good candidate for testing a theory that the young Earth may have been supplied with organic materials (compounds of carbon and hydrogen) and water from asteroids like Bennu colliding with our planet, during a period called the “Late Heavy Bombardment” between 3.8 and 4.1 billion years ago.

We know that during this period, the moon, as well as Earth and the other planets of the inner solar system, were showered by large numbers of asteroids and comets—a fact that our moon and the planets Mercury and Mars testify to with tens of thousands of ancient impact craters.

The materials carried by the impacting objects became part of the makeup of Earth’s crust, and are thought to have supplied some or much of Earth’s surface water and the organic compounds that set the stage for the appearance of life.

Have Comets Fallen Out of Favor?

For many years, comets were singled out as a likely source of Earth’s water and organic materials. Comets are composed largely of water ice and chemicals like ammonia. More recently, we’ve also discovered organic hydrocarbon compounds mixed in.

Attempts to match the chemical signatures of the water in Earth’s ocean with the water-ice in comets have yielded mixed results. Of several comets from which measurements have been obtained—most recently comet 67P/Churyumov-Gerasimenko visited by the European Rosetta spacecraft in 2014—a trend has developed that points away from comets as a significant source of Earth’s fertile starting point.

At the same time, the detection of water ice and carbon compounds within some asteroids has revealed that they are not merely bone-dry hunks of rock and metal as once assumed, strengthening the argument favoring asteroids as the main contributors of those precious materials. In 2015 NASA’s Dawn spacecraft discovered that the former asteroid (now dwarf planet) Ceres may contain a mantle of ice greater in mass than all of Earth’s fresh water.

Asteroids: Friend or Foe?

Recently there has been a lot of concern over the probabilities of Near-Earth Asteroids (of which Bennu is one) colliding with Earth and wreaking havoc and devastation to humans, Earth’s ecosystems, and even our civilization.

It is amusing to think that the first spacecraft mission sent to one of these potential Earth-colliding, flying mountains is aimed at understanding how objects such as these may have brought life to Earth in the first place.

Now that OSIRIS-REx has completed its slingshot maneuver past Earth, it should be smooth sailing all the way to Bennu. NASA will use the time to test the health of its systems and functions. Then, next August when the spacecraft is a little more than a million miles from the asteroid, it will use its thrusters to match course and speed with the asteroid to set up for a final approach.

Humans trekking around Mars just became more realistic. It’s not reality quite yet, but a new virtual reality experience released by Google in partnership with NASA, called Access Mars, is a step in that direction.

The web-based virtual reality (VR) experience lets you explore selected locations visited by NASA’s Curiosity rover along its five-year, nearly 11-mile path of discovery. It not only lets you move about the landscape–poking your nose into highly detailed images of whatever catches your interest–but the 3D terrain model shows relationships between geographical and geological features as no 2D snapshot can.

To recreate the 3D terrain of the chosen sites, data from Curiosity’s stereoscopic camera system was used to derive a topographical model of the landscape, over which the real imagery is mapped. Curiosity becomes your guide on Mars, letting you see our neighboring world almost as if you are there.

Walking on an Ancient Lake Bed?

Curiosity landed in Mars’ Gale Crater in August 2012, during a mission to determine if, and to what extent, liquid water may have been present in Mars’ past. The detection of possible water-associated minerals, like hematite, by NASA’s Mars Reconnaissance Orbiter suggested that the 90-mile wide impact crater may have been a lake.

Not long after its arrival, Curiosity found evidence of past stream bed activity in layers of sedimentary rock made from sand and gravel not far from its landing site, Yellowknife Bay.

As the rover made its way along the crater floor and up the lower slopes of Mount Sharp–a 3.5-mile tall mound of layered sediments at the crater’s center–evidence of past water action mounted.

The Kimberley Formation strata of water-deposited rock slopes downward toward the crater’s center, telling a story of water flowing into Gale Crater before the layers of Mount Sharp had built up.

Fine sediment layers in the Murray Buttes were left behind after a stream delta emptied into standing waters along a shoreline, then dropped the sediment onto the lake floor.

As you explore Access Mars, keep in mind that it’s not just an alien desert you’re setting your virtual footsteps upon, but a water-sculpted milieu that may have once resembled familiar Earthly aquatic scenes.

Curiosity Is Currently Exploring Vera Rubin Ridge

Curiosity is currently exploring a rock formation called Vera Rubin Ridge, after reaching the ridge’s foot in September and beginning an ascent of its slopes.

The location is one that scientists wanted a closer look at even before Curiosity’s landing five years ago. Orbital detection of hematite, an iron oxide mineral that may have been formed in water, made Vera Rubin Ridge a priority destination in Curiosity’s itinerary.

From a distance, down slope, pictures of the ridge revealed repeating horizontal layers in the rock, cross-cut by veins of white material suspected to be calcium sulfate. Whether the horizontal layers of sediment were laid down by water or wind action may be determined when Curiosity gets a closer look, but the veins of calcium sulfate would have been deposited by mineral-laden water flowing through cracks in the rock.

What Will You Find on Mars?

Sometimes what we find in our explorations depends on what we are looking for. When you prospect in a desert, you expect to find sand, rocks, dust, and grit—and maybe even hope to find gold. But when you hike along a dry lake bed, you may see past mere sand and rock to the watery environment that formed them.

With lakes and streams in mind, take a walk with Access Mars, and see what you find.

In October, astronomers discovered that our solar system has been visited by an interstellar traveler. It’s not a spaceship — because that would be truly huge news — but a natural object: a 500-foot chunk of material designated as A/2017 U1.

It is still big news since A/2017 U1 is the first large object passing through our solar system that we know originated in interstellar space.

We Almost Missed It!

At the time it was discovered on October 19, by Robert Weryk using the Pan-STARRS telescope in Hawaii, A/2017 U1 had already swung through its closest approach to our sun — “perihelion” — and was moving away.

But astronomers tracking its movement were able to plot its trajectory, which led to the revelation that A/2017 U1’s orbit is hyperbolic — definitive proof of its interstellar origin.

Unlike the orbits of planets, comets, and asteroids that perpetually run laps around our sun on closed, elliptical loops, a hyperbolic path is “open,” like a boomerang with infinitely long ends. The middle of the boomerang’s bend is where the object makes its closest approach to the sun.

Interstellar Comet or Asteroid?

A/2017 U1 was originally classified as a comet since its hyperbolic path resembles the orbits of “long-period” comets that travel very far into space, but are otherwise gravitationally bound to the sun and orbit it in a regular cycle.

Comets are common fare in regions far from the sun, where sunlight is weak and volatile ices can remain frozen and stable. Almost all of the comets that swing close to the sun spend most of their time in the Kuiper Belt beyond Neptune’s orbit, or in the much more distant Oort Cloud, which surrounds the solar system like a vast, frosty bubble. It is only when a comet heats up near the sun that some of its ices are vaporized and out-gas to form its long, iconic tail.

However, when astronomers pored over data acquired by the SOHO spacecraft around the time of A/2017 U1’s perihelion, no comet-like behavior was detected in the sun’s vicinity. At its closest approach the object was only 23 million miles from the sun, closer than the planet Mercury and within SOHO’s field of view. If it were a comet, SOHO should have detected out-gassing caused by the sun’s intense heat.

The lack of out-gassing shows that A/2017 U1 contains little if any frozen volatile materials, and must be composed of rock or metal — like an asteroid. We are accustomed to thinking of asteroids as objects that spend most of their time relatively close to the sun, where the steady and strong sunlight vaporizes any ices. Objects that originate farther out tend to be comets, containing substantial amounts of ice.

So, discovering an interstellar object that has spent probably hundreds of thousands of years in cold interstellar space, and yet is not a comet but an asteroid, is an even more exciting event.

Where Did A/2017 U1 Come From?

The “legs” of A/2017 U1’s hyperbolic orbit — the long, stretched arcs of the boomerang’s ends — point in the directions it came from and where it is now heading toward, respectively.

The object appears to have cruised in from the direction of the constellation Lyra, somewhere near the star Vega. This doesn’t mean that it originated at Vega, or from any of the stars in that region of the sky.

At its interstellar cruising speed of 16 miles per second, it would take almost 300,000 years to travel the 25 light years from Vega to our solar system. In that time, the stars have moved along their own paths, rearranging themselves in space and making it nearly impossible to determine A/2017 U1’s true point of origin.

It’s likely that this asteroid did originate in a star system long ago and was ejected into interstellar space. It has been theorized that even in our solar system, comets and asteroids have been flung into interstellar space by the gravitational influence of giant planets, like Jupiter. Such evictions would have been especially frequent when the solar system was young and there were many more chunks of rock and ice flying about.

So, it can go both ways: we were just buzzed by an interstellar asteroid that probably came from another star system, and somewhere else in the galaxy a comet or asteroid that originated in our own solar system, flung out millions or billions of years ago, may be whizzing past another star.

NASA Has Dabbled in Interstellar Trajectories

Though A/2017 U1 is a natural object, and not an alien spacecraft like the one featured in Arthur C. Clarke’s novel, “Rendezvous With Rama,” there is, in fact, at least one known spacecraft in interstellar space: our own Voyager 1, which we launched back in 1977.

Voyager 1 officially entered interstellar space in 2013 when it passed through the heliopause, the tenuous boundary between the bubble of gases blown out by our sun and what lies beyond.

In fact, Voyager 1 achieved solar escape velocity in the same way that in theory A/2017 U1 escaped from its parent system: through interaction with a massive planet — in Voyager 1’s case, Jupiter.

Before its encounter with Jupiter, Voyager 1 lacked the speed to break free of the sun’s gravitational pull, but after accelerating under Jupiter’s gravity it was flung into a hyperbolic orbit and became, as NASA put it, “. . . destined — perhaps eternally — to wander the Milky Way.”

But, just as with A/2017 U1, interstellar distances are vast, and the journey between stars is slow.

Voyager 1 is expected to reach our solar system’s cometary haven, the Oort Cloud, in 300 years, and then spend 30,000 years passing through it. In 40,000 years, Voyager 1 will pass within 1.6 light years of the star Gliese 445, enacting its own extrasolar rendezvous.

In the meantime A/2017 U1 is heading out again. As of November 10 it is over 160 million miles from the sun and hurtling away at 25 miles per second.

So, whatever it is — asteroid, or alien artifact — it won’t be pass by ever again.

An ambitious space mission is in the works that promises to reveal extraordinary unseen wonders of the universe. Unseen, literally; the mission, named LISA, is an instrument designed to detect not light waves, but gravitational waves. These are rippling undulations in the very fabric of space produced by bizarre events like merging black holes, colliding neutron stars, and supernova explosions.

LISA (the Laser Interferometer Space Antenna) is a mission of the European Space Agency, in collaboration with NASA, now under development. LISA’s launch will take place sometime in the early 2030s.

Once deployed in space, LISA will consist of three spacecraft separated by millions of miles, linked by a laser beam split between them. Using the technique called laser interferometry, where patterns in the light of combined laser beams signal tiny relative changes in distance, the trio of spacecraft will be able to measure the minute changes in distance between them caused by a passing gravity wave — changes smaller than the diameter of a helium nucleus.

LISA will follow the pioneering programs of ground-based gravity wave detectors, the MIT and Caltech’s twin LIGO installations, and the French-Italian Virgo interferometer.

What are gravity waves?

Gravity waves are fluctuations in spacetime, the name Albert Einstein gave to the “fabric” of the universe “woven” from the three dimensions of space and the one dimension of time.

Einstein’s Theory of Relativity explains gravity not as a force, as Sir Isaac Newton envisioned, but as an effect of the “warping” of spacetime by massive objects within it, like planets, stars and galaxies. Relativity also predicted that the motion of massive objects should produce waves of gravity that move outward, like ripples on the surface of a pool made by something moving in the water.

When a gravity wave passes by a laser interferometer such as LIGO, Virgo, or LISA, the distortion in spacetime causes the distance between the instrument’s mirrors to change minutely, which can be detected in the patterns of the laser beam reflected between.

Imagine a large jello with pieces of fruit and nuts suspended within it. When something causes the jello to jiggle, the distance between the fruit and nuts may change momentarily as the jello is distorted.

Opening Our Ears

For centuries, telescopes have been used to observe electromagnetic waves (light) emitted or reflected by stars, galaxies, planets, comets, asteroids, and clouds of dust and gas, to form pictures of the universe’s visible wonders. But telescopes only let us see places and things where light dares to tread.

Astronomers have long run up against barriers to the perception of light, such as the interiors of black holes, where gravity is so strong that light cannot escape.

Viewing the state of the very early universe, by observing ancient light that has taken billions of years to reach us, also presents a seeing limit, for in its youngest times the hot gases of the primordial universe form an optical “fog” that we cannot see through.

Gravity waves, on the other hand, are not hindered in these ways. When a pair of black holes merge together, the disturbance they cause in spacetime becomes a measurable fluctuation, a gravity wave.

On September 14, 2015, the first gravity wave detection was made, announced in a joint report by LIGO and Virgo scientists.

The wave was produced by the merging of two 30-solar-mass black holes, 1.3 billion light years away, and its observation heralded the beginning of an era in which we can not only see what’s going on in the universe, but in a sense “hear” things as well.

From inside your home, you can see objects all around you — furniture, art, appliances, bookshelves — with your eyes, but what goes on outside may be beyond your sight, hidden behind barriers like walls and landscaping. Still, you know when a big truck rumbles by on the street, or an airplane passes overhead, by the sounds they make.

What can gravity waves tell us about the universe?

Learning about the characteristics of merging black holes and colliding neutron stars are not the only things astronomers hope to achieve with gravity wave instruments like LISA.

Gravity wave observations can give us a better understanding of how the universe has expanded through history, and from that knowledge we may be able to get a stronger grip on the nature of dark energy, the mysterious “anti-gravitational force” that may comprise most of the bulk of the universe.

Scientists may also use this source of observational data to test how gravity behaves over cosmic distances, and whether its strength falls off with distance in any surprising ways — which could reshape our entire understanding of gravity and cosmic physics.

It has also been proposed that gravity waves produced by the core collapse in a supernova explosion may be observable as well.

If so, then astronomers would be able to probe deep inside a supernova as it is happening, another place where light provides no illumination.

For this post-Thanksgiving week, I’d like to suggest a remarkable video produced over two decades by NASA scientists.

Satellites monitored populations of plant life on land and oceans, mapping variations of green regions of vegetation and snow cover on the North and South Poles. As seasons pass, we witness a rhythmic dance between white and green, as if the planet itself were breathing.

Vegetation on land is represented on a scale from brown (low vegetation) to dark green (lots of vegetation). In the ocean, populations of microscopic phytoplankton — a type of algae that uses sunlight to turn water and carbon dioxide into oxygen and sugar — are indicated on a scale from purple (low) to yellow (high).

We see the Earth changing daily and with the seasons as a living planet — its plants, surface winds, and sea currents responding to the energy coming from the sun.

The visualization collated data from Earth-observing satellites like the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), which started collecting data in 1997, and the Terra, Aqua, and Suomi NPP weather satellites.

The changes over the past two decades help scientists understand how the planet is responding both locally and globally to warming trends. Warming ocean temperatures, for example, slow the growth of phytoplankton and, thus, its ability to remove carbon dioxide from the atmosphere. Also visible is the shrinking of the polar caps as the years go by.

Going out into space is not only for the purpose of looking outwards. It allows us to look back at our planet as a whole, follow its changes and rhythms, so that we can better learn how to coexist with it and protect its resources for generations to come.

Marcelo Gleiser is a theoretical physicist and writer — and a professor of natural philosophy, physics and astronomy at Dartmouth College. He is the director of the Institute for Cross-Disciplinary Engagement at Dartmouth, co-founder of 13.7 and an active promoter of science to the general public. His latest book is The Simple Beauty of the Unexpected: A Natural Philosopher’s Quest for Trout and the Meaning of Everything. You can keep up with Marcelo on Facebook and Twitter: @mgleiser

If you recall a 2015 announcement by NASA celebrating the discovery of liquid water on Mars seeping down dusty slopes in dark streaks, you may remember a hubbub of excitement over the possibility of finding life-friendly environments there.

Hitting fast-forward on Martian exploration to the present, a recent study suggests that the rumor of “Martian mud” may not hold as much water as first thought….

The study looks at 3D topography data from NASA’s Mars Reconnaissance Orbiter to explain the streaks not as flowing water stains, but as downhill flows of sand and dust–and has thrown a dry blanket over the quest to find life-friendly environments on Mars.

It’s also a reminder that the walk of scientific exploration is often slow and ponderous, replete with unexpected twists and turns along the path, false trails, and dead ends.

Mysterious Dark Streaks—Wet or Dry?

The mysterious downhill-running streaks were discovered in images captured by NASA’s Mars Reconnaissance Orbiter in 2011, and stirred up a lot of excitement. The streaks, called “recurring slope lineae,” seemed to indicate the potential that liquid water flowed on Mars, and raised the possibility of environments suitable for microbial life. Since their initial discovery, scientists have observed thousands of these streaks in dozens of sites ranging from Mars’ equatorial region to mid latitudes.

The behavior of the streaks looks similar to seasonal snow-melt runoff on Earth, appearing only during warm seasons, growing gradually in the downhill direction in stripes 2-15 feet wide and hundreds of feet long, and then disappearing when the active flow is over.

Then, in 2015, NASA’s Mars Reconnaissance Orbiter detected the presence of hydrated salts in one of the streaks–an unambiguous signal that water, if only in the form of mineral-bonded water molecules, was a player in this mysterious drama.

The discovery not only showed that water molecules were present, it provided fuel for scientists trying to explain how any liquid water could exist under the conditions of Mars’ cold, dry, thin atmosphere. While fresh water should freeze to ice or evaporate into a gas in the Martian desert, salty water can act like an antifreeze, possibly allowing water to flow as a liquid brine for a time.

Flowing Behavior More Like Sand?

The newer research examined 151 recurring slope lineae using 3D image data obtained by the HiRISE camera on the Mars Reconnaissance Orbiter. Analysis revealed that the streaks only appear on slopes steeper than 27 degrees. This small fact is dramatic because that exact degree of slope is the tipping point when a pile of dry dust and sand lying stably on a hillside begins to slide and cascade downhill.  This is called the dynamic “angle of repose.”

The streaks appeared on the steeper slopes, but stopped upon reaching inclines of 27 degrees or less. If flowing water were driving the action, the streaks would not be halted by the gentler slope and would flow on.

Have Visions of a Watery Mars Dried Up?

While the preponderance of evidence gathered by multiple robotic orbiters, landers, and rovers still tells us that, in Mars’ past, liquid surface water was widespread and long-enduring, the search for moisture on Mars today remains a bit of a cat-and-mouse game.

A vast amount of frozen water exists on Mars, under the dusty patina of the flat northern plains and piled up in the polar ice caps—remnants of rivers, lakes, and seas in Mars’ warmer, wetter past eons ago.

As Mars lost the atmospheric swaddling of its youth—through processes under investigation—its water became locked up as ice or evaporated into the thin atmosphere as water vapor. Today, the environment on Mars is far drier than the most parched desert on Earth, where one can still expect to find a bit of morning dew.

A Unique Phenomenon of an Alien Environment?

But the mystery of Mars’ seasonal dark streaks is not completely solved. Questions remain.

Why do the streaks appear only in the warm season, as if triggered by a changing environmental condition? On Earth, seasonally occurring landslides are usually associated with water—precipitation or snow melt causing a hillside to slough off under the added weight and softening soil.

Why do the Martian streaks appear to form gradually, like the slow seeping of water, and not in one quick slide of sand? Landslides of dry dust, soil, and rock on Earth tend to happen in rapid bursts, and then are done.

How does the presence of hydrated salt minerals in the streaks fit into the puzzle? Are salt-bearing soils, upturned and exposed to the atmosphere in a natural landslide, chemically drawing water molecules from the air, as salt tends to do? Or does the hydration of soil salts, maybe driven by elevated seasonal humidity, somehow trigger a slide?

Why do the dark streaks then fade, as if drying up?

Really good questions. Scientists are looking for answers. The more we learn about the phenomenon, the more it seems that it may be a uniquely Martian thing, the likes of which we don’t find on Earth.

Further observations from orbit may help us solve some of these riddles, but the best way to see what is really going on would be to send a lander or rover directly to an area with RSL activity to do some first-hand digging.

This would be a special challenge since these streaks appear only on steep slopes, terrain that we have never attempted to land or drive a robot on. Still, getting there could answer a lot of intriguing questions.

NASA’s Kepler mission announced in December the discovery of an eighth planet orbiting Kepler 90, a sun-like star located about 2,500 light years from Earth.

The discovery is noteworthy not only for the fact that Kepler 90 possesses as many planets as our own solar system, but also for how NASA made the discovery: using artificial intelligence.

Mining Data for Exoplanet Gems

“Training” special AI software, developed by Google, to recognize the elusive signals produced by extrasolar planets (exoplanets), NASA set the AI loose on data collected years ago by the Kepler mission.

The Kepler spacecraft, launched in 2009, searched for exoplanets using the Transit Method: looking for the slight dimming in a star’s light caused by an orbiting planet crossing in front of it (transiting). Kepler continually measured the brightness of 150,000 individual stars near the constellation Cygnus for three years, beaming the data back to Earth for analysis and storage.

Conventional analysis of Kepler’s observations ultimately revealed seven planets in the star system called Kepler 90. But the system’s eighth planet, named Kepler 90i, went undetected–until the AI took a crack at it.

Finding a Needle in a Haystack

Detecting the minuscule dimming in a star’s light caused by a small transiting exoplanet may be likened to searching for a needle in a haystack—a monumental task for a human, though not so difficult for a well-trained, artificially intelligent computer. Once the AI learns the shape and appearance of a needle, it’s just a matter of examining each straw of hay in the stack, one by one, until it finds any that look like a needle. A computer can do that kind of repetitive task without tiring, and do it very quickly.

Kepler 90i is a super-Earth-sized world, with about 1.32 times the diameter of Earth. Orbiting its sun-like star eight times closer than the Earth orbits the sun, Kepler 90i’s surface temperature is estimated to be 817 degrees Fahrenheit. At present, that’s about all we know about it—other than the fact that it orbits its star once in less than 15 days!

How Many Exoplanets Have We Found?

Despite the similarities between detecting exoplanets and finding haystack-embedded needles, conventional analysis has found—quite a lot of needles since the first exoplanet discovery in 1992.

As of December 21, 2017, astronomers have confirmed more than 3,500 exoplanets in 2,660 star systems, with an additional 4,500 candidates awaiting confirmation. Of the confirmed exoplanets, 2,431 of the discoveries are attributed to the Kepler spacecraft.

Of the exoplanets confirmed to exist, 882 are classed as Terrestrial, or approximately the same size as the Earth. And of these Earth-sized worlds, six are located within their stars’ “habitable zones,” which means they’re at the right distance for liquid water to possibly exist on their surfaces.

These known exoplanetary systems represent only a tiny fraction of the stars in the Milky Way galaxy. Extrapolating from the abundance of planets in this small sampling, astronomers estimate there may be billions of Earth-sized exoplanets within the habitable zones of their stars.

Take a breath and let that sink in….

The application of “teachable” AI software to dig through stacks of transit data opens even more possibilities for discovering elusive extrasolar worlds.

Though Kepler 90i was found by fine-sifting through old data, this only means that there may be more—perhaps many more—exoplanets laying hidden on hard drives, waiting to be found.

And now NASA has the AI tool to do the sifting.

NASA’s next Mars mission, InSight — designed to probe unseen depths on the Red Planet — has passed its latest check up and is readying for a spring launch.

The lander passed the crucial test of unfolding twin, origami-like solar panel arrays on January 23. Under illumination simulating Mars’ relatively weak daylight, InSight generated ample electrical power to run its systems.

With a planned May launch fast approaching, and a landing expected in November, engineers are busy putting the robot through its final readiness tests to ensure its survival in the remote wilderness of Mars.

So far, all systems go!

Seeing Within

Unlike past missions, InSight (Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport) will focus on the interior of Mars, and not merely send us pictures of sculpted desert landscapes or analyses of Martian minerals scooped off the ground or drilled from rocks. Those are aspects of Mars’ outer surface, which represents only a tiny fraction of the planet’s overall physique— so, one could argue that we know as little about Mars as medieval physicians knew of the human body, before they began probing inward with surgery.

To get under Mars’ skin, InSight will use an unusual set of scientific instruments, called SEIS, HP3, and RISE.

SEIS (Seismic Experiment for Interior Structure) is a seismometer that will listen for tectonic vibrations caused by possible Marsquakes,  magma movement, meteorite impacts, and the gravitational influence of Mars’ larger moon, Phobos. How vibrations move through Mars can yield clues about its interior structure and composition.

So, imagine that medieval physician putting an ear to a patient’s chest or stomach, and learning something about the location and function of heart and stomach by what they hear.

HP3 (Heat Flow and Physical Properties Package) is a burrowing probe that will tunnel as deep as 16 feet below the surface, pulling a string of temperature sensors behind it. The sensors will measure the rate at which heat flows out of Mars to the surface.

Measurements from HP3 will give insight into the history of heat escaping from Mars — how quickly the core and mantle have cooled, and how this may have shaped the volcanic and tectonic evolution of the planet.

Borrowing again from a medical analogy, modern forensic medical examiners use measurements of body core temperature to estimate time of death.

RISE (Rotation and Interior Structure Experiment) will measure the shift in frequency of InSight’s X-band radio waves to make precise measurements of motion — the motion of the lander, and by extension the Martian surface it rests on. RISE will look for small “wobbles” in Mars’ rotation, telltale “shimmies” that provide clues about its internal structure — not unlike how a washing machine in its spin cycle may vibrate or wobble in a particular way depending on the weight and balance of the laundry inside.

Combined with other measurements of Mars’ rotation made by earlier missions, the size and composition of this planet’s core may be deduced  providing a window into how not only Mars, but all the rocky planets formed.

Rounding out the medical analogies, the technique used in RISE may be likened to a medical Doppler ultrasound, which uses the shift in frequency in sound waves to measure motions within a body. But that’s only an analogy, so don’t work it too hard. . . .

The Fruits of Past and Current Expeditions

Each lander or rover that has set down on Mars has offered something new in our understanding of our neighboring planet — and even though their investigations have been limited to Mars’ surface, their discoveries have been colossal.

The twin Viking landers gave us our first pictures from the surface — something that we are now very familiar with, but which was an epic event in 1976.

The Sojourner rover, the first mobile lander, was able to travel to selected rocks and analyze their composition, the way a human geologist might move around a landscape investigating points of geological interest.

The Mars Exploration Rovers (Spirit and Opportunity) prospected over wide ranges with rock drills and microscopes to paint pictures of Mars’ watery, probably more Earthlike past.

The Mars Science Laboratory (Curiosity) took on the challenge of scaling a mountain to investigate layers of sedimentation laid down over billions of years of Mars’ history, further opening the window to a young Mars possessing rivers, lakes, and seas of liquid water.

Phoenix struck ice!

Scientists are by no means finished exploring Mars’ surface — there’s still a lot it can tell us. But with InSight, they will now be able to peel back the skin and get a peek at Mars’ guts.

Researchers using NASA’s Chandra X-ray Observatory have announced the discovery of a huge assortment of extrasolar planets ranging in size from Earth’s moon to the planet Jupiter.

An extrasolar planet, or exoplanet, is any planet found outside of our own solar system.

The announcement was made by Xinyu Dai and Eduardo Guerras of the University of Oklahoma’s Department of Physics and Astronomy, and published in The Astrophysical Journal Letters on February 2nd.

On its face, this news may not seem extraordinary; these days, announcements of new exoplanet discoveries come out monthly, if not weekly.

The jaw-dropper here is where they were found: in a very distant galaxy, 3.8 billion light years away, wandering free as “rogue” planets in the darkness between the galaxy’s stars. Even more mind-blowing, the observational data indicates that there may be as many as 2,000 of them for every star in that galaxy.

Meaning, trillions.

How Do We Know?

In a galaxy that is 3.8 billion light years away, even individual stars cannot be seen — only the combined luminous “smudge” of multitudes of stars. So how is it possible to detect much smaller, non-luminous objects like planets at that distance?

The short answer is that this wouldn’t be possible, were it not for a phenomenon called gravitational lensing: the bending and focusing of light from a distant object by the gravitational field of another, intervening object.

The phenomenon can be likened to how a glass hand lens bends and focuses light, magnifying a light source — but in this case the “lens” is the gravitational field of a massive object in space.

Gravitational lensing was predicted by Einstein’s theory of Relativity, and has been observed and tested for decades. On a grand scale, gravitational lensing by enormous clusters of galaxies has been observed to magnify much more distant, background galaxies, yielding not only images of the background objects, but a measure of the lensing cluster’s mass based on the degree of light bending.

On a smaller scale, within our own galaxy, astronomers have detected almost a dozen exoplanets through gravitational lensing — or microlensing, in the case where the lensing object is a single star or planet.

The first detection came in 2003, when an object named OGLE 2003-BLG-235 passed between Earth and a more distant star. As it passed, the object’s gravity bent and focused the star’s light toward us, temporarily magnifying it.

The amount of amplification of the star’s light allowed astronomers to calculate the interposing object’s mass as 1.5 times that of Jupiter, which in turn identified it as a planet (as opposed to something more massive, like another star).

But the detection of a single exoplanet by the gravitational microlensing of a single star’s light is a game that can only be played within our own galaxy, at distances where a singular star can be observed.

Detecting exoplanets across 3.8 billion light years is a whole different ballgame.

Window Into Another Galaxy

Dai and Guerras took advantage of the microlensing phenomenon on a grand scale, using the Chandra X-ray Observatory to measure the emissions of a quasar positioned behind their target galaxy. A quasar is the extremely luminous core of a galaxy with an active, supermassive black hole at its center.

Analyzing the X-ray data from the background quasar, they searched for microlensing effects caused by any objects within the intervening galaxy, and a pattern emerged — one that could only be explained by the presence of large numbers of planet-sized objects, drifting independently between the galaxy’s stars.

Though no individual exoplanets were spotted — the distance is too great for that — the patterns produced by multitudes of planetary bodies revealed the exoplanet population.

To push an analogy, if you’ve ever seen a halo around the sun then you might get a sense for how these exoplanets were detected.

A sun halo is formed by the combined bending (or refraction) of sunlight caused by multitudes of water droplets or ice crystals in the atmosphere between you and the sun. Though the droplets are too small and too far away for you to see, their combined effect on the sunlight makes their presence known, and the size and colors of the halo can indicate the properties of the refracting particles.

In a sense, the X-rays shining from the background quasar passed through a “mist” of exoplanets, and the pattern of their combined microlensing effects revealed them to us.

Conventional Exoplanet Discoveries

Until now, all the confirmed detections of exoplanets, numbering more than 3,600, are located inside our Milky Way galaxy, and almost all of these orbit stars.

In fact, it is because these exoplanets orbit stars that we can detect them at all. The two main ways for finding exoplanets, the “radial velocity” and “transit” methods, depend on it.

These methods have turned up thousands of exoplanets in the Milky Way — especially the transit method, which NASA’s ace exoplanet hunter, the Kepler spacecraft, has used to confirm 2,341 of all known exoplanets (as of February 8).

The estimate of 2,000 rogue exoplanets for every star in that distant galaxy is an astounding figure. It means that there may be trillions of planets floating around that one galaxy.

Does this mean that other galaxies possess similar populations of rogue planets? Is our own Milky Way galaxy filled with unseen, dark worlds lurking in the space between the stars?

It has been estimated that there are more stars in the universe than grains of sand on all of Earth’s beaches.

Move over stars; you may be far outnumbered by planets!

The hunt for exoplanets has mostly been an exercise in counting pale, barely distinguishable dots spinning anonymously in space — until now. New and soon-to-come telescopes will have the ability to recognize signals of possible life on planetary cousins outside our solar system, without ever leaving Earth.

At a panel of the American Association for the Advancement of Science Meeting in Austin, Texas this weekend, astronomers spoke wistfully of technological capabilities just around the corner.

“For the first time,” said Aki Roberge, research astrophysicist at NASA’s Goddard Space Flight Center, “we actually have the information to design an experiment that can answer an ages old question, like, ‘Are there worlds like Earth among the stars and do any of them have life?’”

Roberge is the chief scientist helping design a space observatory called LUVOIR that would be a sort of super-charged Hubble, able to study the chemistry of planetary atmospheres outside our solar system — exoplanets — in the clearest detail yet.

While LUVOIR would also be tasked with other astronomical quests (such as studying the formation and evolution of galaxies) the Habitable Exoplanet Imaging Mission would, for the first time, be specially designed to directly image, with an optical/infrared space-based telescope, Earth-like exoplanets. If built, it will be the most sensitive instrument yet to detect signatures of habitability, such as water, on Earth-sized planets around Sun-like stars. If HabEx or LUVOIR can find carbon dioxide, methane, water or oxygen in planetary atmospheres it could indicate the planet is hosting life.

Planning teams for these possible future missions will submit interim studies to NASA in March. The studies will be available to the public shortly after.

A Deluge of Exoplanet Data

Once upon a time, the existence of planets beyond our solar system was an open question. Now, instruments like the Kepler Space Telescope find so many planets so frequently that astronomers are struggling to keep up.

“There are more observations than we can actually get to in real time,” said Jessie Christiansen, staff scientist at NASA’s Exoplanet Science Institute in Pasadena, Calif.

For instance, Christiansen told the audience at the AAAS meeting, NASA’s K2 mission had just (on Thursday, February 15) confirmed 95 new exoplanets. But those discoveries, she said, were based on data from the first two and a half years of K2 data — the current mission of the Kepler Space Telescope.

“And we’re actually at the end of year four,” she said. “So you can see we’re getting a bit behind.”

The growing menagerie of exoplanets — 3,700 at latest count —  almost beggars belief. (And the estimation of possible trillions of free-wandering “rogue” planets is beyond what researchers like Christiansen and Roberge expected when they set out in their careers.)

“It’s absolutely amazing, the reality of what exists out there in worlds among the stars,” said Roberge. “They’re far more abundant, far more diverse than even, I think, the dreams of science fiction.”

Out there, spinning in the dark expanse of space, are large rocky planets known as super-earths, aquatic water worlds, gas dwarfs or superdense diamond planets.

We now know there are multi-planet systems aside from our own. Seven Earth-size planets, all mostly made of rock, huddle around the star TRAPPIST-1. Since the announcement of their discovery last year in February 2017, scientists have taken a closer look at the system. Research released early this month suggests some of the planets in the system could harbor liquid water, perhaps far more than the oceans of Earth.

The first confirmed extra-solar planet was 51 Pegasi b; it was then an entirely new class of planet called a “hot Jupiter.” Based on their density and size, astronomers believe planets like 51 Pegasi b are large and gassy (similar to Jupiter) but based on their closeness to stars, the surface should be feverishly hot.

Yet our characterizations of these planets is still relatively primitive. Researchers make educated guesses about the composition of a planet based on their density and closeness to their star. Whether they have liquid water or signs of microbial activity is unknown.

NASA’s Hubble Space Telescope has tried to take an early look at the atmospheres of these planets, but it’s not exactly designed for the job, being a general purpose (though phenomenally successful) telescope. It was able to rule out the presence of hydrogen in three of the TRAPPIST-1 planets, but not able to search for heavier gases, such as carbon dioxide, methane, water, and oxygen.

NASA’s Transiting Exoplanet Survey Satellite, slated to launch in the coming weeks, will primarily be a tool for counting and locating exoplanets. The James Webb Space Telescope, scheduled to launch in 2019, will follow up on exoplanets of interest and characterize atmospheric gases to a degree. To really see Earth-sized exoplanets up close and personal, though, astronomers will have to wait for LUVOIR or HabEx.

“Now we can say most stars have planets,” said Yale astronomy professor Deborah Fisher at AAAS. “We have to admit the possibility that life may be more common than we guessed.”

NASA launched another of the world’s most advanced weather satellites on Thursday, this time to safeguard the western U.S.

The GOES-S satellite thundered toward orbit aboard an Atlas V rocket, slicing through a hazy late afternoon sky. Dozens of meteorologists gathered for the launch, including TV crews from the Weather Channel and WeatherNation.

GOES-S is the second satellite in an approximately $11 billion effort that’s already revolutionizing forecasting with astonishingly fast, crisp images of hurricanes, wildfires, floods, mudslides and other natural calamities.

The first spacecraft in the series, GOES-16, has been monitoring the Atlantic and East Coast for the past year for the National Oceanic and Atmospheric Administration . The same first-class service is now coming to the Pacific region.

Besides the West Coast, Alaska and Hawaii, GOES-S also will keep watch over Mexico and Central America. It will become GOES-17 once reaching its intended 22,000-mile-high orbit over the equator in a few weeks, and should be officially operational by year’s end.

“We can’t wait!” tweeted the National Weather Service in Anchorage just before liftoff.

With these two new satellites, NOAA’s high-definition coverage will stretch from the Atlantic near West Africa, a hotbed for hurricane formation, all the way across the U.S. and the Pacific out to New Zealand.

It’s the third weather tracker launched by NASA in just over a year: “three brilliant eyes in the sky,” as NOAA satellite director Stephen Volz puts it. GOES-16 launched in late 2016 and an environmental satellite rocketed into a polar orbit from California last November.

These next-generation Geostationary Operational Environmental Satellites, or GOES, are “a quantum leap above” the federal agency’s previous weather sentinels, Volz said. This is the 18th launch of a GOES since 1975; one was lost in a launch explosion and all but three of the satellites are retired.

Even as it was still being checked in orbit, GOES-16 provided invaluable data to firefighters battling blazes in Texas, Oklahoma and elsewhere last March and to Houston-area rescue teams in the flooded aftermath of Hurricane Harvey last August, according to officials. GOES-16 also observed the uncertain path of Hurricanes Irma and the rapidly intensifying Hurricane Maria in September.

GOES-16 “turned out to be better than we expected it to be,” said National Weather Service director Louis Uccellini, on hand for Thursday’s launch. The satellite wasn’t officially on duty yet, “and we were just standing there gawking at the imagery,”

Predicting Bad Weather
As Hurricane Harvey approached the Texas coast, the satellite revealed the clouds sinking in the eye and the eye expanding as the storm morphed from a category 2 to 4, Uccellini said. Those images helped determine when it was safe for rescue teams to go out and save stranded residents, he added.

The satellite also alerted authorities in Texas and Oklahoma to the eruption of new blazes even before the 911 calls came in, Uccellini said. He said the satellite also tracked the direction of the fires like never before, prompting first responders to later tell NOAA: “You saved lives.”

Two more are planned in this four-satellite series: GOES-T in 2020 and GOES-U in 2024. The $10.8 billion cost includes the development, launch and operation of all four satellites as well as ground systems through 2036.

Five months after the Cassini spacecraft’s fiery burnup in Saturn’s atmosphere, the mission continues to make remarkable discoveries about the gas giant planet and its entourage of fascinating moons.

A trove of data sent back to Earth over Cassini’s productive 13-year career remain as digital unexplored territory that scientists continue to investigate. It will be many years before another Saturn mission is mounted, and Cassini’s posthumous bequest of data will not only deliver further rewards, it may help shape that next mission’s scientific goals.

The latest discovery comes from Saturn’s largest moon, Titan, and adds to an impressive list of similarities between this small world and the planet Earth.

Precision measurements of the surface elevations of Titan’s three large liquid-methane seas reveal that they share a common “sea level.” That may not sound remarkable — until you learn that these three seas, unlike the four contiguous oceans on Earth, are not physically connected on the surface, but separated by dry land.

Titan’s Liquid Surprises

It may sound like a page from a far-out science fiction novel, but the fact that there is liquid flowing on Titan’s surface (and falling from its skies) is not new information. Inspiring to the imagination, yes, but not new.

Early in Cassini’s mission following its 2004 arrival at Saturn, the Cassini spacecraft, as well as the European Huygens probe it sent to Titan’s surface, discovered networks of what looked like drainage channels feeding into wide, flat areas — later confirmed to be lakes and seas. At Titan’s surface temperature of minus 290 degrees Fahrenheit, it was obvious that these were not rivers and seas of liquid water, but cryogenic liquid hydrocarbons, mainly methane and ethane.

Flashes of sunlight reflecting from sea surfaces also helped confirm the presence of the surface liquid. Further measurements of Titan’s atmosphere and its thick layer of hydrocarbon haze (natural smog) revealed a complete liquid cycle of precipitation (methane rain!), runoff, and pooling. In addition to the larger lakes and seas, smaller “alpine” lakes were detected at higher elevations, in Titan’s mountains.

Is Titan’s Crust Porous, Like a Sponge?

Now, after over 13 years and 127 flybys of Titan, Cassini has revealed that Titan’s three large seas, Kraken Mare, Ligeia Mare, and Punga Mare, all share a common surface sea level, even though they appear physically separated by dry land—bedrock of water ice and frozen hydrocarbon compounds.

Earth’s oceans are physically connected at the surface, forming one global body of water whose surface naturally seeks a common “equipotential surface” shaped by the forces of Earth’s gravity and rotation.

Explaining Titan’s common sea level requires scratching beneath the surface a bit. Lacking any visible connections on the surface, Titan’s seas must be connected underground, maybe through a system of aquifers or networks of caves.   

While this liquid-leveling interaction between Titan’s seas may function differently than in Earth’s oceans, there is a connection to be made to some of Earth’s lakes. While lakes can be found at many different elevations above sea level on Earth (and Titan, for that matter), some pairs and groups of adjacent terrestrial lakes share common surface levels by “communicating” with each other through underground caves, aquifers, and ground water tables.

So not only has Cassini revealed something new about Titan from beyond the grave, the implications of the discovery tell us something about the composition and structure in Titan’s crust, beneath the surface: it is liquid-permeable over the vast region on which its three large seas rest.

It’s also a reminder that while Titan may resemble Earth in several ways, it’s also a very alien world whose bedrock is water ice and frozen hydrocarbons and whose clouds, rain, rivers, lakes and seas are a frigid liquefied form of natural gas.

Nothing conveys the excitement of space exploration like pictures from another planet. Now NASA is planning to go one better than pictures. The space agency is aiming to launch a probe carrying a communication system that will let future missions to Mars transmit live, high definition video to Earth.

So when the first person walks on Mars, the live video should be far better than what the world saw when Neil Armstrong stepped onto the moon.

NASA has already demonstrated it can now send high definition video from the moon. In 2013, NPR reported on the Lunar Laser Communication Demonstration project.

As the name suggests, the system used laser light to transmit a video from the moon to Earth in real time.

Using light to transmit information at high speeds is nothing new. You might have fiber optic cables carrying the Internet to your house. But in space, light doesn’t travel by cable. A laser is used to send the light signals.

Sending a signal from the moon is one thing. Sending one from Mars is much harder.

“The biggest challenges, by far, have to do with distance,” says Kevin Kelly, CEO of LGS Innovations in Herndon, Va., just outside Washington, D.C. The moon is only about 240,000 miles from Earth. Mars is on average 140 million miles away.

Kelly’s company is building a part of the Deep Space Optical Communications package NASA is planning to put on the Psyche mission that will travel out past Mars.

From Mars, Earth appears as a small dot. “Keeping [a laser] pointed in the right direction and receiving a strong signal is going to be a physics challenge for sure,” Kelly says.

Laser Hiccup
There’s one curious problem when pointing a laser from such a great distance. Even travelling at the speed of light, a laser beam can take as long as 20 minutes to go from the Earth to Mars.

“You may receive the signal from the Earth, but you can just point back in the direction that you got the signal from,” says David Israel, principal investigator on NASA’s Laser Communications Relay Demonstration mission.

Because by the time your transmission gets to where the Earth is, the Earth has moved out of the beam. You have to point it to where the Earth is going to be when the light signal arrives. This “point ahead” system is like throwing a pass to a receiver in football. If the receiver is running down the field, the quarterback has to throw it to where the receiver is going to be when the ball gets there.

One of the challenges of deep space laser communications is capturing all the light that’s sent. To do that, NASA will be using the historic 200-inch Hale telescope on Mt. Palomar in California. The captured light will go into a detector that’s being built at NASA’s Jet Propulsion Laboratory in Pasadena.

The detectors can measure a single photon of light. “With these detectors we can detect these very faint signals that are going to coming back from this laser transmitter,” says JPL physicist Matt Shaw.

NASA’s not just interested in using laser communication from deep space. Laser systems can transmit much more data than a radio signal, so they could replace traditional radios on spacecraft.

Space Communication
At MIT’s Lincoln Laboratory, engineers are building a miniature system they’re planning to send into low Earth orbit space next year.

“The data rates that we’re aiming for this demonstration are 200 gigabits per second, 200 billion bits per second,” says Brian Robinson, associate group leader of the optical communications technology group at the lab.

And with a laser in low Earth orbit, you don’t need a big telescope to capture the photons. “Between 4 to 8 inches,” he says, “maybe as large as a foot. In other words, about the size of a hobbyist’s telescope.”

Using light to transmit data and video may be the future of space communications, but it’s actually quite an old idea. Alexander Graham Bell, the inventor who brought us the telephone, built something called the photophone in the 1880s that transmitted sound using light from the sun.

“Bell demonstrated it right here in Washington, D.C., between a laboratory that was on the roof of a school just near the White House over to his laboratory that was just a few blocks away,” says LGS Innovations’ Kelly.

Talk about an inventor ahead of his time.

NASA plans to launch its new deep space laser communication system in 2022.

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